> Christian Heimes added the comment:
> 
> This small change also changes behavior of OpenSSL dramatically. What
> are your Python and OpenSSL versions? 

I tested by compiling my own python3 (8aaf499) against its parent (d6d344d) For python2, I made the same by compiling the 2.7.13 as a baseline and results were consistent with the python I have on Ubuntu 17.10 (3.5.3 and 2.7.13).

> How did you profile the
> performance of the hashing functions?

I compared the timings between my patched vs patchless python versions by using a 630MB file to calculate sha256 as:

perf stat -r 10 Python-2.7.13/python -c "import hashlib; print(hashlib.sha256(open('ubuntu-16.10-server-ppc64el.iso','rb').read()).hexdigest())"

The speedup of ~50% is given due to patchless taking 3.082156387s and patched taking 2.027484800s (errors are less than 1%)

I also noticed what changed on a code level by checking with gdb what is being executed on the sha loop. After my patch I see altivec (SIMD) functions being used on SHA main loop.

> If OpenSSL_config() really improves performance on relevant platforms,
> then we should be consistent and call it in _ssl.c, too.

I'll check that then. Thanks for the hint.

Ps: please note this behavior is noticed on a POWER8 machine. I'm not an OpenSSL expert so I don't know if there are now more optimizations enabled on other architectures as well.